Magnetic Resonance Imaging (MRI) measures the presence of polarized particles within objects and processes these measurements into images showing the location and concentrations of the particles. A magnetic field is applied to an object to align the particles within the object along a direction of the magnetic field. Once the particles are aligned, the object is subjected to a radio frequency (RF) pulse with or without using magnetic field gradients. This pulse deflects the particles from their axis. In returning to their axes (i.e., during relaxation), the particles emit a signal that can be measured by magnetic field receptors, such as coils. The detected signals are used to produce images of the object.
Some noble gases are both effective anesthetic agents and suitable for use in MRI systems. One noble gas with known anesthetic properties that has been approved for use in humans is Xenon. In addition, 129Xenon (129Xe) has non-zero nuclear spin, making 129Xenon theoretically suited to MRI. The small magnetic moment, however, of 129Xenon makes it, in its normal state, impractical for use in MRI. Helium, in particular 3Helium (3He) is another noble gas adapted for use in MRI.
Both 129Xenon and 3He have been shown to be practical for MRI use when hyperpolarized. Hyperpolarizing 129Xenon or 3He increases the nuclear spin and enhances the signal produced during relaxation compared to when these gases are not hyperpolarized. These gases can be hyperpolarized ex vivo using, e.g., well-known optical pumping techniques, and have relatively long relaxation times in vivo, enhancing their usefulness for in vivo MRI.